This invention relates to a process for coordination polymerization of olefins using metallocenes having pendant, boron based Lewis acid groups.
Boron based Lewis acids having fluorinated aryl substituents are known to be capable of activating transition metal compounds into olefin polymerization catalysts. Trisperfluorophenylborane is taught in EP 0 520 732 to be capable of abstracting a ligand for certain cyclopentadienyl derivatives of transition metals while providing a stabilizing, compatible noncoordinating anion. The term xe2x80x9cnoncoordinating anionxe2x80x9d is now accepted terminology in the field of olefin polymerization, both by coordination or insertion polymerization and carbocationic polymerization. See, for example, EP 0 277 004, U.S. Pat. No. 5,198,401, and Baird, Michael C., et al, J. Am. Chem. Soc. 1994, 116, 6435-6436, and U.S. Pat. No. 5,668,324. The noncoordinating anions are described to function as electronic stabilizing cocatalysts, or counterions, for cationic metallocene complexes which are active for olefin polymerization. The term noncoordinating anion as used here applies both to truly noncoordinating anions and coordinating anions that are at most weakly coordinated to the cationic complex so as to be labile to replacement by olefinically or acetylenically unsaturated monomers at the insertion site.
Organoaluminum compounds are known to be useful with metallocene based transition metal cationic catalysts, as cocatalyst activators, or for those stabilized with noncoordinating anions, for both catalyst poison inhibition and alkylation of metallocene dihalide compounds, see WO 91/14713 and EP 0 500 944. See also WO 93/14132 where alumoxane compounds are said to be useful for inhibiting catalyst poisons in the presence of cationic, cyclopentadienyl Group 4 complexes activated by tris(perfluorophenyl)boron.
Certain metallocene compounds having pendant, boron based Lewis acid groups are described by R. E. v. H. Spence and W. E. Piers in xe2x80x9cToward One-Component Group 4 Homogenous Ziegler-Natta Olefin Polymerization Catalysts: Hydroboration of Zirconium bisalkyl with Pendant 2-Propenyl Groups Using [(C6F5)2BH]2xe2x80x9d, Organometallics 1995, 14, 4617-4624. As indicated in the title, compounds having boron based Lewis acids having fluorinated aryl substituents linked to cyclopentadienyl ring carbon atoms via hydroboration of propenyl groups that are pendant to cyclopentadienyl ligands are disclosed. It is suggested that these compounds will have utility as zwitterionic, self-activating catalysts. See also the zwitterionic catalysts of U.S. Pat. No. 5,792,819 where pendant, boron based Lewis acid groups are attached to a Group 4 metal center.
The synthesis of Group 13-based compounds derived from trisperfluorophenylborane are described in EP 0 694 548. These compounds are said to be represented by the formula M(C6F5)3 and are prepared by reacting the trisperfluorophenylborane with dialkyl or trialkyl Group 13-based compounds at a molar ratio of xe2x80x9cbasically 1:1xe2x80x9d so as to avoid mixed products, those including the type represented by the formula M(C6F5)nR3-n, where n=1 or 2. Utility for the trisaryl aluminum compounds in Ziegler-Natta olefin polymerization is suggested.
The invention comprises a process for the preparation of polyolefins from one or more olefinic monomers comprising combining said olefins with a novel catalyst complex derived from: i) a metallocene catalyst compound having a Group 13-15 bridging element substituted with a Group 13 moiety containing two halogenated aromatic groups, and ii) an alkyl aluminum compound or aluminoxy derivative thereof. In the invention, the pendant, Lewis acidic Group 13 moiety is bonded to the metallocene through the bridging Group 13-15 atom that is also covalently bonded to at least one cyclopentadienyl ring atom of a metal ligand and to a second ancillary metal ligand that may be another, same or different, cyclopentadienyl ring ligand or a heteroatom ligand of the same metal center. Increased activities, over those with similar metallocenes not having the pendant boron groups and similarly activated with alumoxane compounds, have been observed with the invention catalysts.